The invention relates to a color television camera comprising a plurality of pickup elements. Each pickup element converts an optical image on a pickup area of the pickup element into an electric picture signal. The optical images are obtained by an optical color separation system provided in an optical path of scene light.
The camera comprises a test image projector for producing a test image on the pickup areas via the optical color separation system. The camera comprises an adjusting circuit coupled to the pickup elements for obtaining, with the aid of the test images, synchronous picture signals with optimum picture coverage on joint display.
Such a color television camera is disclosed in French Pat. No. 1,577,746. More specifically, FIG. 3 of that patent shows the color separation system and the test image projector. Herein, a wheel, provided with a transparent optical filter plane and an opaque plane which has a reflecting surface on the side facing the color separation system, is arranged in front of a light entrance face of the color separation system.
During scene recording, the transparent filter plane of the wheel is present in the optical path to the color separation system. During synchronization of the picture signals (that is to say that upon a collective display of the adjusted picture signals to obtain optimum registration), the opaque plane of the wheel is present as a shutter in the optical path, thus blocking light coming from the scene. The test image is then projected to the reflecting wheel plane, which reflects the light from the test image in the direction of the optical axis to the light entrance face of the color separation system. As a result, the test images and the scene pictures are produced on the pickup areas of the pickup elements along the same optical axes. In the drawing the wheel is provided between an optical lens system and the optical color separation system.
Arranging the reflecting shutter between the optical lens system and the optical color separation system is considered to be a disadvantage, as it is desirable to keep the optical path as short as possible. When the optical path is kept as short as possible, a more compact construction is obtained so that less imaging errors occur in the optical path.
Advantageously, the shutter is arranged before the optical lens system, but the presence of the wheel then interferes with adjustment of the lens system. So as to enable an unobstructed rotation of the wheel between the lens system and the color separation system, prior to and after adjustment of the lens system, some mechanical tolerance is necessary, which again increases the length of the optical path.